The invention relates to stable aqueous dispersions based on fine-particled (co)polymers of styrenes and/or of acrylic and/or methacrylic acid esters which, when dried as a film, have increased resistance against hydrolysis owing to the special manufacturing process.
In U.S. Pat. No. 2,227,163, a process has already been proposed for the polymerization, at elevated temperature, of monomeric compounds in the presence of a high-molecular-weight polyvinyl alcohol or a water-soluble derivative thereof, with the aid of hydrogen peroxide. Carrying out that process with the monomers of the present invention resulted, however, in completely useless dispersions full of a coarse-grained coagulate. In particular, dispersions having solids contents of greater than 35% by weight, especially greater than 40% by weight, could not be prepared without those dispersions suddenly becoming rheopectic or coagulating.
From GB-PS 1 155 275, on the other hand, a process is known for the manufacture of copolymers in which latices are first prepared in the presence of an emulsifier and, at conversions of from 20% to 80%, a protective colloid, such as polyvinyl alcohol, is added. In that case, the polyvinyl alcohol serves only as an additional stabilizer. It is not possible, according to that process, to manufacture stable dispersions with the protective colloid being added earlier since the mixture then coagulates (Comparison Test B).